Light-emitting diodes (LEDs) have become ubiquitous in the electronics world, where they are utilized as light sources in a wide variety of applications. Some specific examples include the use of LEDs as indicators and in electronic displays. More recently, the use of LEDs has expanded to such products as traffic control systems, street lighting, spot lighting for home and industrial applications and automobile headlights.
FIG. 1 illustrates a typical diode 111 of the type used in an LED module. The diode 111, which may comprise a semiconductor material such as AlGaAs, has a P-type region 113 and an N-type region 115 defined thereon. The P-type region 113 and the N-type region 115 are equipped with electrodes 117 and 119, respectively, and are separated by a junction 121 across which a depletion zone 123 exists. When the electrode 119 in contact with the N-type region 115 is positively charged (thereby serving as an anode) and the electrode 117 in contact with the P-type region 113 is negatively charged (thereby serving as a cathode), free electrons and holes accumulate on opposing sides of the diode, thus widening the depletion zone 123. This process causes free electrons moving across the diode 111 to fall into empty holes from the P-type region 113, with an associated drop in the energy of the electrons from a conduction band to a lower energy band. The energy released by this process is emitted as photons. Due to the particular band gap in AlGaAs and other semiconductor materials commonly used in LEDs, the frequencies of the emitted photons fall within the visible region of the spectrum. Hence, when suitably harnessed, this phenomenon can be used to create LED light sources.
FIG. 2 depicts a typical LED module which incorporates a diode of the type depicted in FIG. 1. As seen therein, the LED module 131 comprises a diode 133 to which is connected first 135 and second 137 terminals. The diode 131 is enclosed within a housing 139. The housing 139 is constructed such that light emitted from the diode 133 which impinges on the side 141 of the housing will be reflected, while light impinging on the top 143 of the housing 139 will be transmitted. Consequently, the diode 133 acts as a directional light source.
Due to their unique structure, LEDs have certain advantages over other known light sources such as fluorescent lamps, incandescent lamps and mercury lamps. In particular, LEDs do not utilize a filament. Hence, compared to filament-based light sources, illumination devices equipped with LEDs are more compact and, at least potentially, have much longer life spans.
At present, heat dissipation is one of the major obstacles currently facing commercial applications of LEDs, especially in applications that involve the use of LEDs as illumination sources. While LEDs have been demonstrated to have lifetimes of 50,000 hours or greater, their lifetimes drop off sharply with increases in operating temperature. Thus, in one study reported in the literature, lifetimes in LED modules were observed to drop more than 7-fold when the operating temperatures of the modules were raised from 25° C. to 90° C.
In a typical LED, a significant portion of the current that is applied to the electrodes is subsequently converted into thermal energy. In lighting applications, the amount of thermal energy generated is significant, due to the number of lumens that the LED module must generate. Consequently, in order to maintain the illumination source at an acceptable operating temperature and to thereby achieve an adequate lifetime for the system, such an illumination source must be equipped with an efficient heat dissipation system.
Some attempts have been made in the art to equip LED modules with thermal management systems. These approaches typically involve the installation of a heat sink on the back of a substrate to which the LED is mounted. The heat sink is then used in conjunction with a heat dissipation system such as a fan or a piezoelectric jet actuator. However, while this approach does dissipate some of the heat generated by the LED module, it also increases the size and/or footprint of the module. Consequently, this approach compromises the compactness of the LED module, which is one of the major advantages of LED light sources. Moreover, the use of fans or piezoelectric devices to cool the heat sink is undesirable in that these devices generate noise, while most lighting applications require silent operation. Furthermore, in many applications such as ceiling mounted lighting, spatial constraints dictate a low product profile. In such applications, the attachment of a heat sink to the back of the device provides no benefit, since there is no means for entraining cool air or for disposing heated air into the ambient environment.
There is thus a need in the art for a means for efficiently and quietly dissipating heat generated by an LED module, and for an LED module that incorporates such a means. There is further a need in the art for such an LED module that is compact and offers flexibility of positioning. These and other needs are met by the devices and methodologies described herein.